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Threonine
Threonine
(symbol Thr or T[2]) is an amino acid that is used in the biosynthesis of proteins. It contains an α-amino group (which is in the protonated −NH+ 3 form under biological conditions), a carboxyl group (which is in the deprotonated −COO− form under biological conditions), and a side chain containing a hydroxyl group, making it a polar, uncharged amino acid. It is essential in humans, meaning the body cannot synthesize it: it must be obtained from the diet. Threonine
Threonine
is synthesized from aspartate in bacteria such as E. coli.[3] In the genetic code it is encoded by the codons ACT, ACC, ACA, and ACG. Threonine
Threonine
sidechains are often hydrogen bonded; the most common small motifs formed are based on interactions with serine: ST turns, ST motifs (often at the beginning of alpha helices) and ST staples (usually at the middle of alpha helices).

Contents

1 Modifications 2 History 3 Biosynthesis 4 Metabolism 5 Sources 6 References 7 External links

Modifications[edit] The threonine residue is susceptible to numerous posttranslational modifications. The hydroxyl side-chain can undergo O-linked glycosylation. In addition, threonine residues undergo phosphorylation through the action of a threonine kinase. In its phosphorylated form, it can be referred to as phosphothreonine. It is a precursor of glycine, and can be used as a prodrug to reliably elevate brain glycine levels. History[edit] Threonine
Threonine
was the last of the 20 common proteinogenic amino acids to be discovered. It was discovered in 1936 by William Cumming Rose[4], collaborating with Curtis Meyer. The amino acid was named threonine because it was similar in structure to threose, a four-carbon monosaccharide with molecular formula C4H8O4[5]

 

L- Threonine
Threonine
(2S,3R) and D- Threonine
Threonine
(2R,3S)

 

L-allo- Threonine
Threonine
(2S,3S) and D-allo- Threonine
Threonine
(2R,3R)

Threonine
Threonine
is one of two proteinogenic amino acids with two chiral centers, the other being isoleucine. Threonine
Threonine
can exist in four possible stereoisomers with the following configurations: (2S,3R), (2R,3S), (2S,3S) and (2R,3R). However, the name L-threonine is used for one single diastereomer, (2S,3R)-2-amino-3-hydroxybutanoic acid. The second stereoisomer (2S,3S), which is rarely present in nature, is called L-allo-threonine. The two stereoisomers (2R,3S)- and (2R,3R)-2-amino-3-hydroxybutanoic acid are only of minor importance.[citation needed] Biosynthesis[edit] As an essential amino acid, threonine is not synthesized in humans, and needs to be present in proteins in the diet. Adult humans require about 20 mg/kg body weight/day.[6] In plants and microorganisms, threonine is synthesized from aspartic acid via α-aspartyl-semialdehyde and homoserine. Homoserine
Homoserine
undergoes O-phosphorylation; this phosphate ester undergoes hydrolysis concomitant with relocation of the OH group.[7] Enzymes involved in a typical biosynthesis of threonine include:

aspartokinase β-aspartate semialdehyde dehydrogenase homoserine dehydrogenase homoserine kinase threonine synthase.

Threonine
Threonine
biosynthesis

Metabolism[edit] Threonine
Threonine
is metabolized in two ways:

In many animals it is converted to pyruvate via threonine dehydrogenase. An intermediate in this pathway can undergo thiolysis with CoA to produce acetyl-CoA and glycine. In humans the gene for threonine dehydrogenase is an inactive pseudogene[8], so threonine it is converted to α-ketobutyrate. The mechanism of the first step is analogous to that catalyzed by serine dehydratase, and the serine and threonine dehydratase reactions are probably catalyzed by the same enzyme.[9]

Sources[edit] Foods high in threonine include cottage cheese, poultry, fish, meat, lentils, Black turtle bean[10] and Sesame
Sesame
seeds.[11] Racemic
Racemic
threonine can be prepared from crotonic acid by alpha-functionalization using mercury(II) acetate.[12] References[edit]

^ Dawson, R.M.C., et al., Data for Biochemical Research, Oxford, Clarendon Press, 1959. ^ "Nomenclature and Symbolism for Amino Acids and Peptides". IUPAC-IUB Joint Commission on Biochemical Nomenclature. 1983. Archived from the original on 9 October 2008. Retrieved 5 March 2018.  ^ Raïs, Badr; Chassagnole, Christophe; Lettelier, Thierry; Fell, David; Mazat, Jean-Pierre (2001). " Threonine
Threonine
synthesis from aspartate in Escherichia coli
Escherichia coli
cell-free extracts: pathway dynamics" (PDF). J Biochem. 356: 425–32. PMC 1221853 . PMID 11368769.  ^ A Dictionary of scientists. Daintith, John., Gjertsen, Derek. Oxford: Oxford University Press. 1999. p. 459. ISBN 9780192800862. OCLC 44963215.  ^ Meyer, Curtis (20 July 1936). "The Spatial Configuation of Alpha-Amino-Beta-Hydroxy-n-Butyric Acid" (PDF). Journal of Biological Chemistry. 115 (3).  ^ Institute of Medicine
Institute of Medicine
(2002). " Protein
Protein
and Amino Acids". Dietary Reference Intakes for Energy, Carbohydrates, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids. Washington, DC: The National Academies Press. pp. 589–768.  ^ Lehninger, Albert L.; Nelson, David L.; Cox, Michael M. (2000). Principles of Biochemistry (3rd ed.). New York: W. H. Freeman. ISBN 1-57259-153-6. . ^ Stipanuk, Martha H.; Caudill, Marie A. (2013-08-13). Biochemical, Physiological, and Molecular Aspects of Human Nutrition - E-Book. Elsevier Health Sciences. ISBN 9780323266956.  ^ Bhardwaj, Uma; Bhardwaj, Ravindra. Biochemistry for Nurses. Pearson Education India. ISBN 9788131795286.  ^ http://ndb.nal.usda.gov/ndb/foods/show/4632?fg=&man=&lfacet=&count=&max=&sort=&qlookup=&offset=&format=Full&new= ^ "SELF Nutrition Data - Food Facts, Information & Calorie Calculator". nutritiondata.self.com. Retrieved 27 March 2018.  ^ Carter, Herbert E.; West, Harold D. (1940). "dl-Threonine". Organic Syntheses. 20: 101. ; Collective Volume, 3, p. 813 .

External links[edit]

Threonine
Threonine
biosynthesis CID 205 CID 6288

v t e

The encoded amino acid

General topics

Protein Peptide Genetic code

By properties

Aliphatic

Branched-chain amino acids (Valine Isoleucine Leucine) Methionine Alanine Proline Glycine

Aromatic

Phenylalanine Tyrosine Tryptophan Histidine

Polar, uncharged

Asparagine Glutamine Serine Threonine

Positive charge (pKa)

Lysine
Lysine
(≈10.8) Arginine
Arginine
(≈12.5) Histidine
Histidine
(≈6.1)

Negative charge (pKa)

Aspartic acid
Aspartic acid
(≈3.9) Glutamic acid
Glutamic acid
(≈4.1) Cysteine
Cysteine
(≈8.3) Tyrosine
Tyrosine
(≈10.1)

Amino acids
Amino acids
types: Encoded (proteins) Essential Non-proteinogenic Ketogenic Glucogenic Imino acids D-amino acids Dehydroamino acids

v t e

Amino acid
Amino acid
metabolism metabolic intermediates

K→acetyl-CoA

lysine→

Saccharopine Allysine α-Aminoadipic acid α-Ketoadipate Glutaryl-CoA Glutaconyl-CoA Crotonyl-CoA β-Hydroxybutyryl-CoA

leucine→

β-Hydroxy β-methylbutyric acid β-Hydroxy β-methylbutyryl-CoA Isovaleryl-CoA α-Ketoisocaproic acid β-Ketoisocaproic acid β-Ketoisocaproyl-CoA β-Leucine β-Methylcrotonyl-CoA β-Methylglutaconyl-CoA β-Hydroxy β-methylglutaryl-CoA

tryptophan→alanine→

N'-Formylkynurenine Kynurenine Anthranilic acid 3-Hydroxykynurenine 3-Hydroxyanthranilic acid 2-Amino-3-carboxymuconic semialdehyde 2-Aminomuconic semialdehyde 2-Aminomuconic acid Glutaryl-CoA

G

G→pyruvate→citrate

glycine→serine→

3-Phosphoglyceric acid

glycine→creatine: Glycocyamine Phosphocreatine Creatinine

G→glutamate→ α-ketoglutarate

histidine→

Urocanic acid Imidazol-4-one-5-propionic acid Formiminoglutamic acid Glutamate-1-semialdehyde

proline→

1-Pyrroline-5-carboxylic acid

arginine→

Agmatine Ornithine Citrulline Cadaverine Putrescine

other

cysteine+glutamate→glutathione: γ-Glutamylcysteine

G→propionyl-CoA→ succinyl-CoA

valine→

α-Ketoisovaleric acid Isobutyryl-CoA Methacrylyl-CoA 3-Hydroxyisobutyryl-CoA 3-Hydroxyisobutyric acid 2-Methyl-3-oxopropanoic acid

isoleucine→

2,3-Dihydroxy-3-methylpentanoic acid 2-Methylbutyryl-CoA Tiglyl-CoA 2-Methylacetoacetyl-CoA

methionine→

generation of homocysteine: S-Adenosyl methionine S-Adenosyl-L-homocysteine Homocysteine

conversion to cysteine: Cystathionine alpha-Ketobutyric acid+Cysteine

threonine→

α-Ketobutyric acid

propionyl-CoA→

Methylmalonyl-CoA

G→fumarate

phenylalanine→tyrosine→

4-Hydroxyphenylpyruvic acid Homogentisic acid 4-Maleylacetoacetic acid

G→oxaloacetate

see urea cycle

Other

Cysteine
Cysteine
metabolism

Cysteine
Cysteine
sulfinic acid

v t e

Glycine
Glycine
receptor modulators

Receptor (ligands)

GlyR

Agonists: β-Alanine β-ABA (BABA) β-AIBA Caesium D-Alanine D-Serine GABA Glycine Hypotaurine Ivermectin L-Alanine L-Proline L-Serine L-Threonine MDL-27531 Milacemide Picolinic acid Propofol Quisqualamine Sarcosine Taurine

Positive modulators: Alcohols (e.g., brometone, chlorobutanol (chloretone), ethanol (alcohol), tert-butanol (2M2P), tribromoethanol, trichloroethanol, trifluoroethanol) Alkylbenzene sulfonate Anandamide Barbiturates (e.g., pentobarbital, sodium thiopental) Chlormethiazole D12-116 Dihydropyridines (e.g., nicardipine) Etomidate Ginseng
Ginseng
constituents (e.g., ginsenosides (e.g., ginsenoside-Rf)) Glutamic acid
Glutamic acid
(glutamate) Ivermectin Ketamine Neuroactive steroids (e.g., alfaxolone, pregnenolone (eltanolone), pregnenolone acetate, minaxolone, ORG-20599) Nitrous oxide Penicillin G Propofol Tamoxifen Tetrahydrocannabinol Triclofos Tropeines (e.g., atropine, bemesetron, cocaine, LY-278584, tropisetron, zatosetron) Volatiles/gases (e.g., chloral hydrate, chloroform, desflurane, diethyl ether (ether), enflurane, halothane, isoflurane, methoxyflurane, sevoflurane, toluene, trichloroethane (methyl chloroform), trichloroethylene) Xenon Zinc

Antagonists: 2-Aminostrychnine 2-Nitrostrychnine 4-Phenyl-4-formyl-N-methylpiperidine αEMBTL Bicuculline Brucine Cacotheline Caffeine Colchicine Colubrine Cyanotriphenylborate Dendrobine Diaboline Endocannabinoids (e.g., 2-AG, anandamide (AEA)) Gaboxadol
Gaboxadol
(THIP) Gelsemine iso-THAZ Isobutyric acid Isonipecotic acid Isostrychnine Laudanosine N-Methylbicuculline N-Methylstrychnine N,N-Dimethylmuscimol Nipecotic acid Pitrazepin Pseudostrychnine Quinolines (e.g., 4-hydroxyquinoline, 4-hydroxyquinoline-3-carboxylic acid, 5,7-CIQA, 7-CIQ, 7-TFQ, 7-TFQA) RU-5135 Sinomenine Strychnine Thiocolchicoside Tutin

Negative modulators: Amiloride Benzodiazepines (e.g., bromazepam, clonazepam, diazepam, flunitrazepam, flurazepam) Corymine Cyanotriphenylborate Daidzein Dihydropyridines (e.g., nicardipine, nifedipine, nitrendipine) Furosemide Genistein Ginkgo constituents (e.g., bilobalide, ginkgolides (e.g., ginkgolide A, ginkgolide B, ginkgolide C, ginkgolide J, ginkgolide M)) Imipramine NBQX Neuroactive steroids (e.g., 3α-androsterone sulfate, 3β-androsterone sulfate, deoxycorticosterone, DHEA sulfate, pregnenolone sulfate, progesterone) Opioids (e.g., codeine, dextromethorphan, dextrorphan, levomethadone, levorphanol, morphine, oripavine, pethidine, thebaine) Picrotoxin
Picrotoxin
(i.e., picrotin and picrotoxinin) PMBA Riluzole Tropeines (e.g., bemesetron, LY-278584, tropisetron, zatosetron) Verapamil Zinc

NMDAR

See here instead.

Transporter (blockers)

GlyT1

ACPPB ALX-1393 ALX-5407 (NFPS) AMG-747 ASP2535 Bitopertin
Bitopertin
(RG1678/RO4917838) CP-802079 Ethanol (alcohol) Glycyldodecylamide GSK1018921 LY-2365109 ORG-24598 ORG-25935
ORG-25935
(SCH-900435) PF-02545920 PF-03463275 PF-04958242 Sarcosine SSR-103,800 SSR-504,734

GlyT2

Amoxapine Ethanol (alcohol) NAGly Opiranserin (VVZ-149) ORG-25543 VVZ-368

See also Receptor/signaling modulators GABA receptor modulators GABAA receptor positive modulators Ionotropic glutamate r

.